1. Field of the Invention
The present invention relates generally to an apparatus and method for transmitting signals in a communication system, and in particular, to an apparatus and method for transmitting signals using a power amplifier in a communication system.
2. Description of the Related Art
Generally, a Radio Frequency (RF) power amplifier used in the current communication system is classified into a Single-Carrier Power Amplifier (SCPA) and a Multi-Carrier Power Amplifier (MCPA).
Referring to FIGS. 1A and 1B, a configuration of a general communication system using an SCPA will be described herein.
FIGS. 1A and 1B are diagrams schematically illustrating a structure of a signal transmission apparatus with SCPA in a general communication system. Specifically, FIG. 1A is a diagram schematically illustrating a structure of a signal transmission apparatus with an SCPA using a single Frequency Assignment (FA) in a general communication system, and FIG. 1B is a diagram schematically illustrating a structure of a signal transmission apparatus with SCPAs using multiple FAs in a general communication system.
Referring to FIG. 1A, the signal transmission apparatus includes a Single FA input signal Generation Block (SGB) 101, an SCPA 103, a Front End Block (FEB) 105, and an Antenna (ANT) 107.
Referring to FIG. 1B, the signal transmission apparatus includes a plurality of SGBs 111a to 111n, a plurality of SCPAs 113a to 113n, a Channel Combiner (CC) 115, an FEB 117, and an antenna 119.
As illustrated in FIGS. 1A and 1B, when the signal transmission apparatus transmits an RF power signal using an SCPA, it amplifies a single FA in the manner of FIG. 1A. When the signal transmission apparatus with SCPAs uses multiple FAs, it combines FAs amplified independently by the SCPAs using a channel combiner before transmission in the manner of FIG. 1B.
Specifically, shown in FIGS. 1A and 1B, the signal transmission apparatus with SCPA includes as many SCPAs as the number of FAs in use. Thus, when the number of FAs used in an initial system application is small, the signal transmission apparatus with SCPA can be advantageous over the signal transmission apparatus with MCPA in terms of cost competitiveness. The SCPA is optimized for amplifying a single FA. The general communication system, due to its limited number of antennas, should combine outputs of the SCPAs using a channel combiner for channel combination, if the number of FAs in operation increases. However, the channel combiner used at outputs of the SCPAs has a very high insertion loss, and can hardly combine adjacent FAs.
Therefore, when the signal transmission apparatus with SCPA transmits a multi-FA signal for which it should use a channel combiner, the SCPAs transmit the output which is higher than that of the MCPA by an insertion loss of the channel combiner, in order to allow the antenna to transmit the same output power. That is, an increase in the number of the FAs used in the signal transmission apparatus with SCPA causes an increase in the number of the SCPAs. In terms of the same antenna output, the SCPAs, compared with the MCPA, increase in system power consumption due to the insertion loss of the channel combiner, requiring a higher system cooling capability and thus increasing the system operating cost.
Next, with reference to FIGS. 2A and 2B, a structure of a signal transmission apparatus with MCPA in a general communication system will be described herein.
FIGS. 2A and 2B are diagrams schematically illustrating a structure of a signal transmission apparatus with MCPA in a general communication system. Specifically, FIG. 2A is a diagram illustrating a structure of a signal transmission apparatus with MCPA using a single FA in a general communication system, and FIG. 2B is a diagram illustrating a structure of a signal transmission apparatus with MCPA using multiple FAs in a general communication system.
Referring to FIG. 2A, the signal transmission apparatus includes an SGB 201, an MCPA 203, an FEB 205, and an antenna 207. Referring to FIG. 2B, the signal transmission apparatus includes a Multi-FA input signal Generation Block (MGB) 211, an MCPA 213, an FEB 215, and an antenna 217.
As illustrated in FIGS. 2A and 2B, in a communication system, a transmission signal input to an MCPA from a particular transceiver is a multi-FA combined signal, and the MCPA amplifies the input multi-FA signal.
Specifically, in the signal transmission apparatus with MCPA shown in FIGS. 2A and 2B, the MCPA, although it can amplify a single FA, is optimized for amplifying a combined multi-FA signal. In the communication system with limited number of antennas, as the MCPA does not use a channel combiner even though the number of FAs in operation increases, the MCPA, compared with the SCPAs, decreases in power consumption in terms of the same antenna output. Therefore, the MCPA requires a lower cooling capacity, thereby increasing competitiveness in the system implementation cost and the system operating cost.
Generally, however, the MCPA is higher than the SCPA in price per unit, and in a system with less number of FAs in operation, the MCPA uses only its partial capacity inefficiently, thereby increasing the initial system installation cost. In addition, when the system operates with less number of FAs so that it can use the SCPAs without channel combiner, the use of the MCPA is disadvantageous over the use of the SCPAs in terms of the efficiency.
As described above, FIGS. 1A and 1B and FIGS. 2A and 2B show preferred types and structures of RF power amplifiers used in the current communication system. In particular, FIGS. 1A and 1B show a structure of a signal transmission apparatus with SCPA, and FIGS. 2A and 2B show a structure of a signal transmission apparatus with MCPA.
The voice-oriented service of the existing communication system has overcome an inferiority of channels depending on channel coding. However, as a demand for the high-quality multimedia service in the communication system increases, there is a demand for a communication service capable of greatly increasing the communication capacity and improving the call quality by efficiently using the limited spectrum. As a scheme for realizing the demanded communication service, a Smart Antenna scheme and a Multiple Input Multiple Output (MIMO) scheme have been provided and are now under active study.
The communication technology using the Smart Antenna or MIMO scheme necessarily requires a structure that uses a plurality of transmission antennas, so it needs a plurality of RF power amplifiers. In addition, as the transmission bandwidth increases for high-speed data transmission, there is a need for an RF power amplifier for amplifying a broadband signal.
However, when a signal transmission apparatus with Smart Antenna or MIMO scheme is implemented with the existing SCPAs, the signal transmission apparatus uses a plurality of transmission antennas, thus it needs as many SCPAs as the product of the number of FAs and the number of antennas. Therefore, competitiveness of the system considerably decreases in terms of cost, structure and size. In addition, even when the signal transmission apparatus with Smart Antenna or MIMO scheme is implemented with MCPA, the signal transmission apparatus should use a plurality of transmission antennas, so it needs as many MCPAs as the number of antennas, decreasing competitiveness of the system in terms of the cost, structure and size.
In most communication systems, the RF power amplifiers occupy 30% or more of the system space, 50% or more of the system power consumption, and 35% or more of the system cost, so they are very important in terms of system competitiveness. Therefore, there is a need for a scheme of designing a system using a power amplifier capable of solving the problems of the existing system.